GROWTH AND METABOLISM 



115 



conveniently taken first is that of Chlorella vulgaris growing 

 under conditions in which neither carbon nor nitrogen 

 assimilation is limited. ^^^ The changes occurring in the 

 amounts of various components in cultures of this alga are 

 shown in Fig. 16. At the end of the exponential phase (8 



DAYS OF GROWTH 



FIG. 16. Amounts per culture of different components of Chlorella 

 vulgaris, plotted logarithmically and adjusted as to level for 

 comparative purposes. A, disaccharide; B, starch; C, insoluble 

 carbohydrate; D, protein (after ref. 225). 



days) the relative rates of accumulation of both protein and 

 carbohydrate decline but the former decreases more than 

 the latter. Later, when the stationary phase is reached (16 

 days), protein synthesis ceases altogether but starch con- 

 tinues to be accumulated. As a result, cells harvested in the 

 stationary phase are of different chemical composition to 

 those taken at the end of the exponential phase, e.g. at 

 20 days 15-3 per cent of the dry matter is protein and 21-5 

 per cent is starch as compared with 24-4 per cent of protein 

 and 15-5 per cent of starch at 7 days. Corresponding with 



